1. Field of the Invention
The invention relates to a method and an apparatus for regulating the register in a printing press.
2. Description of the Related Art
In case of multi-color printing with rotary printing presses, the colors have to be printed in the respective printing units on top of each other in accordance with register marks. If this is not possible, a dowdy and thus unsellable print is obtained, which means that a loss of material results. During the continuous printing operation, deviations from the register marks may occur due to various reasons. These deviations have to be compensated for in order to obtain a sufficient printing quality. Such deviations of register marks are usually measured by means of a register control device and re-controlled automatically.
A reel fed printing press of the above-mentioned type comprises at least two printing units, wherein each of these comprises at least one cylinder including the printing plate on its surface and a second cylinder, between which the object to be printed, generally a web or a sheet, is passed for being printed.
For this purpose, each printing unit usually co-prints at least one mark. The respective position of this mark is measured relative to a mark printed by another printing unit or another position information from the printing press, e.g. the rotating angle information of one of the aforementioned cylinders. A register correction signal is generated based on the deviation of a target position representing a good printout. This signal is then performed by suitable devices (e.g. register rollers) and thus generates again a printout in accordance with the register marks. Such register control devices are generally known in the related art as evidenced, for example, by EP 0 637 286 B1.
DE 10 2005 019 566 A1 describes a register control device for a gravure printing machine having the typical components, including, for example, one driving unit and one data logging device in each printing unit as illustrated in FIG. 1.
DE 10 2005 054 975 describes a controller system for the register in a printing machine that includes at least one printing unit. The controller system includes at least one register control device, in which a pilot control variable and an register error estimated variable are used for influencing the register. Further, this application teaches that the printing machine has only one single data bus for transmitting the register error estimated variable and the pilot control variable as well as for transmitting rotations speeds and positions for the speed control.
In addition, DE 10 2005 054 975 provides that the estimated error variables, which are the variables to be performed in the individual drives for a register correction, shall be transmitted via a bus. However, the measured register deviation variables are not transmitted despite the fact that the processing of the register deviation variables is nevertheless of equal relevance for a control.
It has proven to be disadvantageous in both aforementioned devices and methods that the data logging devices are directly included into the drive unit, and therewith the measured values for the register positions and register deviations are only generated and present at the printing unit where they are sensed. Consequently, a controller having a decentralized regulating concept is obtained, which may be rather disadvantageous in a variety of applications.
Any additional effort in view of wiring and signal processing, as is required, for example, in the solution of the first-mentioned document, is generally disadvantageous. An avoidance of this disadvantage by using the usual data bus and operating systems is purposeful only to a limited extent, since such systems—despite generally high transmission rates—feature a relative temporal imprecision when exchanging information. Thus, the cycle time of a control cycle is unfortunately limited toward a lower limit and the precision of determining a position is decreased. The use of a driving bus for transmitting correction values, as it is proposed in DE 10 2005 054 975, solves the last-mentioned problem only partially.